Vision guided robotic systems have been employing the principle of optical triangulation to measure surface points on objects to be worked on by a robot. In particular, one arrangement employs the projection of a plane of light that falls upon the object to be measured and forms a line of light on the object surface where the surface intersects the light plane. A TV camera views the line of light from a known angle away from the plane of light, and this forms the basis for computing the location of each point on the line relative to the camera/projector sensor. The TV camera provides a video output signal that is processed to provide these measurements.
In using a sensor of this type, mounted on a robot arm to guide the robot along an edge or seam on an object, it has been necessary to anticipate the sudden loss of measurement data when the corner of the edge is reached or the seam reaches an edge. Since data is only obtained when the plane of light intersects the surface, the data disappears when the plane is carried beyond the corner or edge. The robot is usually fitted with a tool, such as a welding gun, which is being guided by the vision data and which must trail the line of intersection to avoid interfering with the vision measurement. Thus, the tool still has some distance to travel when the guidance data is lost.